Root Knot Nematodes

Nematode damage Photo Credit: Clemson University -  USDA Cooperative Extension Slide Series,

Nematode damage on root (left) vs normal root (right)
Photo Credit: Clemson University – USDA Cooperative Extension Slide Series,

The Integrated Pest Management (IPM) class I took during the Carolina Yard Gardening School was so chock full of knowledge, I had to split the information into three articles! This is the third installment of what I learned in that IPM class. (I did a little additional research on my own, as well, to supplement what I learned.)


Root knot nematodes can be a big problem in the garden, especially in the subtropical zones of the southeastern United States. Yes, where I live and garden. Thankfully, I’ve not had much problem with them, but I know fellow gardeners in the area who have.

So, what are these nasty critters? They are one type of microscopic worm-like critter that can cause severe damage to a crop. Basically, they eat on the roots of the plant, which causes galls or nodules to grow on the roots. This root damage then prevents the plant from taking up sufficient nutrients from the soil, and the plant becomes stunted and doesn’t mature properly. When nematodes are a problem, managing the population becomes necessary.

As discussed in the previous two articles (see links below), Integrated Pest Management uses three types of control, two of which can be used against nematodes:

  • Cultural – what humans can do
  • Biological – what nature can do


There are several things you can do to manage root knot nematodes in your garden.

  • Crop rotation – Rotate your crops from season to season and year to year. Many nematodes like certain plants, so crop rotation can reduce their population.
  • Fallow ground – If you have a large problem, you may want to let your ground lay fallow for a season.
  • Increase organic matter – This is the best defense against root knot nematodes (and other “bad” nematodes). They don’t like fertile soil. Also, beneficial fungi that attack these nematodes thrive in soil that is high in organic matter.
  • Sanitation – Remove all plant debris, including the roots, after harvest. You don’t want to leave food for the nematodes.
  • Resistance – Choose resistant varieties of plants.
  • Soil amendments – Research is showing that soil amendments containing chitin (made from crustacean shells) encourage chitin-eating fungi to reproduce in the soil. These fungi attack the nematode eggs, which are made of chitin.
  • Trap crops – Plant trap crops such as marigolds.

Marigolds contain a chemical that inhibits nematode egg-laying and kills the nematodes themselves. However, only certain species and cultivars of marigolds have this chemical. Because some varieties of marigolds will actually attract the nematodes, you shouldn’t interplant the marigolds with your crop. It’s best to use the correct variety of marigold as a cover crop. Let them grow 3-4 months, then till them under as green manure. For more information on using marigolds to combat nematodes, see the University of Hawaii article, Protecting Crops from Nematode Pests.


There is not much we can do chemically to combat nematodes, but there are some biological controls.

  • Bacteria – Healthy, fertile soil will contain many types of bacteria that will attack root knot nematodes.
  • Fungi – Nematode-trapping fungi are a natural enemy that is useful in the garden. One way to “invite” some to your garden is by adding chitin-containing soil amendments.
  • Parasitic nematodes – Yes, there are beneficial nematodes that kill root knot nematodes. Who knew?

I’m grateful I haven’t had issues with root knot nematodes in my garden. I hope that as long as I keep my soil healthy, fertile, and full of organic matter, I won’t ever have those critters attacking my plant roots.



Have you had any issues with nematodes in your garden?


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